This invention relates to the field of nickel-base alloys possessing resistance to high temperature corrosive environments.
Nickel-base high temperature alloys serve in numerous applications, such as, regenerators, recuperators, combustors and other gas turbine components, muffles and furnace internals, retorts and other chemical process equipment and transfer piping, boiler tubing, piping and waterwall aprons and waste incineration hardware. Alloys for these applications must possess outstanding corrosion resistance to meet the long life requirements becoming critical in new facility design and operation. While virtually all major industrial equipment is exposed to air on one surface or at one part of the unit, the internal surfaces can be exposed to very aggressive carburizing, oxidizing, sulfidizing, nitriding, or combinations of these corrodents. Consequently, maximum corrosion resistance to the broadest possible range of aggressive high temperature environments, is a long-sought aim of the metallurgical industry.
Traditionally, these alloys rely on precipitation hardening from a combination of xcex3xe2x80x2 [Ni3(Al, Ti)], xcex3xe2x80x3 [Ni3(Nb, Al, Ti)], carbide precipitation and solid solution strengthening to give the alloy strength. The xcex3xe2x80x2 and xcex3xe2x80x3 phases precipitate as stable intermetallics that are essentially coherent with the austenitic-fcc matrix. This combination of precipitates significantly enhances the high temperature mechanical properties of the alloy.
It is an object of this invention to provide an alloy that possesses resistance to carburizing, oxidizing, nitriding and sulfidizing environments.
It is a further object of this invention to provide an alloy with sufficient phase stability and mechanical integrity for demanding, high temperature applications.
A nickel-base alloy consisting of, in weight percent, 42 to 58 nickel, 21 to 28 chromium, 12 to 18 cobalt, 4 to 9.5 molybdenum, 2 to 3.5 aluminum, 0.05 to 2 titanium, at least one microalloying agent selected from the group consisting of 0.005 to 0.1 yttrium for carburization resistance and 0.01 to 0.6 zirconium for sulfidation resistance, 0.01 to 0.15 carbon, 0 to 0.01 boron, 0 to 4 iron, 0 to 1 manganese, 0 to 1 silicon, 0 to 1 hafnium, 0 to 0.4 niobium, 0 to 0.1 nitrogen, incidental impurities and deoxidizers.